Concentration profiles in the diffusional film in the calcium carbonate dissolution process

A mass transfer model for determining limestone dissolution rates in aqueous solutions of SO2, based on the Nernst theory of stagnant film, has been developed. The model considers the effects of the equilibrium acid—base reactions and of the diffusive transport of ionic and molecular species between the liquid bulk and the particle surface. The equations of the model have been numerically integrated leading to the concentration profiles of the species in the film around the particle. These profiles show a strong non-linearity in the film and their shape can be explained considering the presence of two reaction zones in the film. Some experimental runs have been carried out in a fixed-bed reactor to evaluate the film thickness under controlled fluid dynamic conditions and with varying liquid compositions. Consistency between experimental and model results, on the basis of the hypothesis of the model, has been found.